Most pharmaceutical solutions and suspensions manufactured on an industrial scale require highly controlled, thorough mixing to achieve a satisfactory yield and ensure a uniform distribution of ingredients in the final product. Agitator tanks are frequently used to complete the mixing process, but a better degree of mixing is normally achieved by using a mechanical stirrer or impeller (e.g., a set of mixing blades attached to a metal rod). Typically, the mechanical stirrer or impeller is simply lowered into the fluid through an opening in the top of the vessel and rotated by an external motor to create the desired mixing action.
One significant limitation or shortcoming of such an arrangement is the danger of contamination or leakage during mixing. The rod carrying the mixing blades or impeller is typically introduced into the vessel through a dynamic seal or bearing. This opening provides an opportunity for bacteria or other contaminants to enter, which of course can lead to the degradation of the product. A corresponding danger of environmental contamination exists in applications involving hazardous or toxic fluids, or suspensions of pathogenic organisms, since dynamic seals or bearings are prone to leakage. Cleanup and sterilization are also made difficult by the dynamic bearings or seals, since these structures typically include folds and crevices that are difficult to reach. Since these problems are faced by all manufacturers of sterile solutions, pharmaceuticals, or the like, the U.S. Food and Drug Administration (FDA) has consequently promulgated strict processing requirements for such fluids, and especially those slated for intravenous use.
In an effort to overcome these problems, others have proposed alternative mixing technologies. Perhaps the most common proposal for stirring a fluid under sterile conditions is to use a rotating, permanent magnet bar covered by an inert layer of TEFLON, glass, or the like. The magnetic “stirrer” bar is placed on the bottom of the agitator vessel and rotated by a driving magnet positioned external to the vessel. An example of such an arrangement where the vessel is not a flexible bag is shown in U.S. Pat. No. 5,947,703 to Nojiri et al., the disclosure of which is incorporated herein by reference.
Of course, the use of such an externally driven magnetic bar avoids the need for a dynamic bearing, seal or other opening in the vessel to transfer the rotational force from the driving magnet to the stirring magnet. Therefore, a completely enclosed system is provided. This of course prevents leakage and the potential for contamination created by hazardous materials (e.g., cytotoxic agents, solvents with low flash points, blood products, etc.), eases clean up, and allows for the desirable sterile interior environment to be maintained, all of which are considered significant advantages.
Despite the advantages of this type of mixing systems and others where the need for a shaft penetrating into the vessel or dynamic seal is eliminated, a substantial, but heretofore unsolved problem with such systems is the difficulty in coupling a fluid-agitating element with an external motive device providing the rotation and/or levitation force. For example, when a vessel in the form of a flexible bag containing an unconfined fluid-agitating element is positioned in proximity to the motive device, the relative location of the fluid-agitating element is generally unknown. In the case of a small (10 liter or less) transparent bag, it is possible to manipulate the bag relative to the motive device in an effort to ensure that the fluid-agitating element is “picked up” and the desired coupling is formed. However, this is considered inconvenient and time consuming, especially if fluid is already present in the bag. Moreover, in the case where the bag is relatively large (e.g., capable of holding 100 liters or more) or formed of an opaque material, achieving the proper positioning of the fluid-agitating element relative to the external motive device is at a minimum difficult, and in many cases, impossible. In the absence of fortuity, a significant amount of time and effort is required to lift and blindly reposition the bag relative to the motive device, without ever truly knowing that the coupling is properly formed. Also, even if the coupling is initially formed, the fluid-agitating element may become accidentally decoupled or disconnected from the motive device during the mixing operation. In view of the semi-chaotic nature of such an event, the ultimate resting place of the fluid-agitating element is unknown and, in cases where the fluid is opaque (e.g., blood) or cloudy (e.g., cell suspensions), not easily determined. If the coupling ultimately cannot be established in the proper fashion, the desired fluid agitation cannot be achieved in a satisfactory manner, which essentially renders the set up useless. These shortcomings may significantly detract from the attractiveness of such fluid agitation systems from a practical standpoint.
In many past mixing arrangements, a rigid vessel is used with a fluid-agitating element directly supported by a post carrying a roller bearing, with the rotational force being supplied by an external device (see, e.g., U.S. Pat. No. 4,209,259 to Rains et al., the disclosure of which is incorporated herein by reference). While this direct support arrangement prevents the fluid-agitating element from becoming lost in the event of an accidental decoupling, the use of such post or like structure in a bag for receiving and holding a fluid-agitating element has not been proposed. The primary reason for this is that, in a typical flexible bag, neither the sidewalls nor any other structure is capable of providing the direct support for the fluid-agitating element or a corresponding bearing.
Thus, a need is identified for an improved manner of ensuring that the desired low friction support is provided for a fluid-agitating element in a vessel, such as a bag, rotated by an external motive device. The improvement provided by the invention would be easy to implement using existing manufacturing techniques and without significant additional expense. Overall, a substantial gain in efficiency and ease of use would be realized as a result of the improvement, and would greatly expand the potential applications for which advanced mixing systems may be used.